An ordinary liquid developer for electrostatic photography is generally prepared by dispersing organic or inorganic pigments or dyes, such as carbon black, Nigrosine, Phthalocyanine Blue, etc., and a natural or synthetic resin such as an alkyd resin, an acrylic resin, rosin, a synthetic rubber, etc., in a high-insulating and low-dielectric constant liquid such as a petroleum aliphatic hydrocarbon and further adding thereto a polarity controlling agent such as a polymer containing a metal soap, lecithin, linseed oil, a higher fatty acid, vinyl-pyrrolidone, etc. In such a liquid developer, a resin is dispersed therein as insoluble latex particles having diameters of several .mu.m to several hundred .mu.m, and since, in a conventional liquid developer, the bonding between a soluble dispersion stabilizing resin or a polarity controlling agent and insoluble latex particles is insufficient, the soluble dispersion stabilizing resin and the polarity controlling agent are in a state of easily diffusible in the liquid. Accordingly, in such a conventional liquid developer, there is a disadvantage that the soluble dispersion stabilizing resin is released from the insoluble latex particles by the storage of the developer for a long period of time or by repeated use of the developer, the cause precipitation, aggregation, or accumulation of the latex particles, whereby the polarity of the liquid developer becomes obscure. Also, since the latex particles, once aggregated or accumulated, are difficult to disperse again, the particles stick to various portions of a developing devince to cause strains of images formed as well as problems of the developing device, such as clogging of a liquid supply pump, etc.
For eliminating these disadvantages, a means for chemically bonding the soluble dispersion stabilizing resin and the insoluble latex particles is disclosed in U.S. Pat. No. 3,990,980.
However, the improvement for the redispersibility, the shelf life, and stability of the liquid developer was insufficient, and the latex particles precipitated or accumulated at various portions of a developing device were solidified in film-form and were difficult to redisperse in the means disclosed in aforesaid U.S. Pat. No. 3,990,980. Also, the particles prepared by the above-described means have two or more peaks in the particle size distribution curve or a broad particle size distribution, and it was difficult to control the particle size of the particles. Thus, the liquid developer containing the particles was also poor in shelf life and stability.